1. Field of the Invention
This invention relates to a sputtering apparatus, and more particularly to such an apparatus which is capable of effectively sputtering by allowing gas pressure to differ from place to place within a vacuum chamber.
2. Description of the Prior Art
Generally in a sputtering apparatus, a target and a substrate to be sputtered are placed in a vacuum chamber containing a gas and a high frequency voltage or a direct current voltage is applied between the target and the substrate to produce a glow discharge and accordingly ionize the gas. Then, the ions impact the target to thereby eject atoms from the target material and allow them to be deposited on the surface of the substrate. Particularly in the process of manufacturing various semiconductor devices, a reactive sputtering technique is used where a reactive gas such as O.sub.2, N.sub.2, etc. is used as the gas of the vacuum chamber so that reaction with the atoms sputtered from the target occurs to produce a layer comprising an oxide, a nitride or the like covering the substrate.
Conventional sputtering apparatuses have been arranged so that the pressure of the gas within the vacuum chamber is substantially uniform. None have been specifically designed so that the gas pressure varies from place to place within the vacuum chamber. The gas pressure affects the sputtering as follows. When the gas pressure is relatively high, the sputtering process becomes active, and a relatively high gas pressure is required in case of reactive sputtering. On the other hand, when the gas pressure is relatively low, the crystallizability and the layer forming efficiency are improved because the amount of resputtering is low.
Such conventional sputtering apparatuses have realized one or the other of the merits described in the above-mentioned cases of high and low pressure, but have not been able to provide all of the merits obtained in both cases.